Maybe some of you already know of ideas such as these have thought about them or have heard about similar sites.

Earlier this year, OneSwitch.org.uk arranged a longer competition together with Retro Remakes, focusing on creating and exploring the idea of "one switch" games. These could be playable by people with disabilities or illnesses that make it impossible for them to play ordinary multi-control games.
All the games released during the competition were targetted towards Windows machines (given as the people on the Retro Remakes forums mostly are Windows programmers). Several of the games were pretty high quality, and implemented the one switch idea in several ways. You can see reviews of some of the finished games from this competition at Acid-Play.

I am sure Barry from OneSwitch.org.uk would love to see more "one switch" games for the Mac as well. If you manage get some good ideas, or produce some interesting tidbits for the Mac during these 24 hours, please consider polishing/finishing your product a little more afterwards once you get the time. If you get a version good enough for people to enjoy and play, let OneSwitch.org.uk know about its existence. You could make some otherwise disadvantaged players very happy.